This application claims the priority of German Patent Document No. 10 2010 015 211.0, filed Apr. 16, 2010, the disclosure of which is expressly incorporated by reference herein.
The invention relates to a damping element for damping rotor blade vibrations of a turbomachine, a rotor blade having this type of damping system, a rotor having a plurality of these types of damped rotor blades and a method for damping rotor blade vibrations of a rotor of a turbomachine.
Rotor blades of gas turbines, such as aircraft engines, are frequently braced with one another within a blade ring via their shrouds to dampen vibrations. To this end, the shrouds have a Z-like design with two respective force transmitting surfaces for mutual mechanical coupling as shown in the Applicant's German Patent No. DE 40 15 206 C1. Even though this type of mechanical coupling is very effective, the shrouds are subjected to a relative high level of wear in the region of the force transmitting surfaces however.
In addition, bracing rotor blades with one another via a wire-like damping element, which is guided through the blade pans, is also known from European Patent Document No. EP 0 511 022 B1. However, the particular disadvantage of this solution is that the wire-like damping element is located in the flow path or annular space channel. This solution is not useable or useable only conditionally in the case of internally cooled blades in particular.
In addition, arranging damping elements in pockets of adjacent shrouds is known from European Patent Document No. EP 1 944 466 A1. When the rotor rotates, the damping elements are moved radially outwardly due to centrifugal force and thereby bring about a mechanical coupling of the shrouds. However, it is not possible to optimally adjust the damping of vibrations with this system.
Furthermore, using a damping system based on centrifugal force is known from U.S. Pat. No. 3,037,741, where the system's damping elements are arranged in a space between two neighboring rotor blades, which is limited in the radial direction by their platforms. The damping elements are displaceably guided respectively via a pin in a rotor bore in the radial direction and can thereby run against lower areas of the platforms during a rotation. However, due to their topology, these types of damping elements do not offer adequate damping of torsional modes of vibration in particular. In addition, the available structural design space is very limited so that the design and size of these damping elements do not meet their design and implementation requirements or only in a conditional manner.
German Patent Document No. DE 30 08 890 discloses a rotor for a gas turbine engine, which has a damping weight for damping purposes, which during rotation is pressed radially outwardly and engages frictionally on the inner surface of a platform.
The object of the present invention is creating a damping system for damping rotor blade vibrations of a turbomachine, a rotor blade with this type of damping system, and a rotor with a plurality of these types of damped rotor blades.
A damping system according to the invention for damping vibrations of a rotor blade of a rotor of a turbomachine, for example of an aircraft engine, has a damping element, which is guided on a rotor-side support in such a way that it executes a radially outwardly directed movement based on centrifugal force during a rotation of the rotor and can be brought into contact with a lower platform area of the rotor blade.
The damping system according to the invention allows a damping of critical modes of vibration of compressor and turbine run stages with and without a shroud, in a mounted designed or integral BLISK (bladed disk) or BLING (bladed ring) design, with or without blade cooling as well as with or without blade hollow spaces. The damping element is guided as a so-called rocking damper on the support such as, for example, a cover plate or a mini-cover plate on the rotor blade. Because of the rotation of the rotor, degrees of freedom of movement of the damping element based on a materializing centrifugal force field are utilized in such a way that a contact is produced on one or more defined couple contact points at least between the rotor blade and the damping element that is automatically reguided by the centrifugal force field. In this case, the mass of the damping element serves as an optimization parameter and to define switching points between a so-called “locked and slipping” state of the damping system.
The damping element may likewise execute movements in the circumferential direction of the rotor so that the damping element has degrees of freedom of movement that are as great as possible.
In the case of one exemplary embodiment, the damping element is mounted on the support by at least one connection element, which is guided into a radially extending longitudinal groove. In this case, the longitudinal groove is preferably designed in such a way that, when the damping element runs onto the lower platform area, the connection element is spaced apart from an opposing wall section of the longitudinal groove (as viewed in the movement direction of the damping element) and thereby released. In other words, the at least one connection element serves merely as a safeguard, and not however as a limit of the radial movement of the damping element. The limit is accomplished by the lower platform area of the blade.
In the case of another exemplary embodiment, the damping element has opposing sliding surfaces for guidance along two support-side, radially-extending guide surfaces. It is likewise conceivable for the damping element to be mounted on the support so it can be swiveled.
The danger of tilting can be further reduced if the damping element is configured to be U-shaped and grips around a head section of the support on both sides.
A circumferential contact surface formed by an elevation is preferably arranged in the lower platform area as a limit stop for the damping element. In addition, a frontal contact surface for producing a frictional contact between the damping element and the rotor blade may be provided. The exact position of the contact surfaces may be adjusted as a function of the respective mode of vibration so that an individualized contacting between the damping element and the rotor blade takes place and vibrations may be damped effectively. In the case of one exemplary embodiment, the contact surfaces are arranged, for example, symmetrically to the longitudinal surface of the damping element.
A rotor blade according to the invention for a turbomachine, for example of an aircraft engine, has at least one damping system with a damping element, which is guided on a rotor-side support in such a way that it executes an outwardly directed movement in the radial direction during a rotation of the rotor and can be brought into contact with a lower platform area of the rotor blade. The damping system may be arranged in the axial rotor direction in front, behind or on both sides, i.e., both upstream as well as downstream from the rotor blade.
A rotor according to the invention for a turbomachine has a plurality rotor blades arranged in blade rows, wherein damping elements are arranged on the rotor blades of at least one blade row, which damping elements are guided in such a way on a rotor-side support that they execute a movement in the radial direction due to centrifugal force and can be brought into contact with a lower platform area of the rotor blades. The damping elements dampen preferably flexural and torsional modes of vibration. In this case, a geometric adaptation of the contact geometry between the damping elements and the rotor blades may optimize or increase the damping effect on the mode of vibration characteristic.
In the case of a method according to the invention for damping vibrations of rotor blades of a turbomachine, for example of an aircraft engine, a damping element is respectively provided in a lower platform area of the rotor blades, which damping element is guided on the rotor-side support and moved against the respective lower platform area due to centrifugal force.
In the case of a preferred exemplary embodiment, the respective damping element rubs along a frontal contact surface of the rotor blades so that with a rotation the damper element is not just pressed on the lower platform area and in frictional contact therewith, but a mechanical damping also occurs through the dissipation of energy because of dry friction between the damping element and the vibrating frontal contact surfaces. As the case may be, a mechanical damping between the damper element and the support also occurs.
Preferred exemplary embodiments of the present invention will be explained in greater detail in the following on the basis of schematic representations.